Systems and methods for providing deeper knee flexion capabilities for knee prosthesis patients

ABSTRACT

Systems and methods for providing deeper knee flexion capabilities, more physiologic load bearing and improved patellar tracking for knee prosthesis patients. Such systems and methods include (i) adding more articular surface to the antero-proximal posterior condyles of a femoral component, including methods to achieve that result, (ii) modifications to the internal geometry of the femoral component and the associated femoral bone cuts with methods of implantation, (iii) asymmetrical tibial components that have an unique articular surface that allows for deeper knee flexion than has previously been available, (iv) asymmetrical femoral condyles that result in more physiologic loading of the joint and improved patellar tracking and (v) modifying an articulation surface of the tibial component to include an articulation feature whereby the articulation pathway of the femoral component is directed or guided by articulation feature.

RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.13/776,637, filed Feb. 25, 2013, and entitled SYSTEMS AND METHODS FORPROVIDING A TIBIAL ARTICULATION FEATURE, which is a continuationapplication of U.S. patent application Ser. No. 12/482,280 (now U.S.Pat. No. 8,382,846), filed Jun. 10, 2009, and entitled SYSTEMS ANDMETHODS FOR PROVIDING DEEPER KNEE FLEXION CAPABILITIES FOR KNEEPROSTHESIS PATIENTS, which is a continuation-in-part of U.S. patentapplication Ser. No. 12/198,001 (now U.S. Pat. No. 8,273,133), filedAug. 25, 2008, and entitled SYSTEMS AND METHODS FOR PROVIDING DEEPERKNEE FLEXION CAPABILITIES FOR KNEE PROSTHESIS PATIENTS, which claimspriority to U.S. Provisional Patent Application Ser. No. 60/968,246,filed Aug. 27, 2007, and entitled SYSTEMS AND METHODS FOR PROVIDINGDEEPER KNEE FLEXION CAPABILITIES FOR KNEE PROSTHESIS PATIENTS, and toU.S. Provisional Patent Application Ser. No. 60/972,191, filed Sep. 13,2007, and entitled SYSTEMS AND METHODS FOR PROVIDING DEEPER KNEE FLEXIONCAPABILITIES FOR KNEE PROSTHESIS PATIENTS, each of which is incorporatedherein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to knee prostheses. In particular, thepresent invention relates to systems and methods for providing deeperknee flexion, or full functional flexion capabilities, more physiologicload bearing and improved patellar tracking for knee prosthesispatients. Specifically, these improvements include (i) adding morearticular surface to the antero-proximal posterior condyles of a femoralcomponent, including methods to achieve that result, (ii) modificationsto the internal geometry of the femoral component and the associatedfemoral bone cuts with methods of implantation, (iii) asymmetricaltibial components that have an unique articular surface that allows fordeeper knee flexion than has previously been available and (iiii)asymmetrical femoral condyles that result in more physiologic loading ofthe joint and improved patellar tracking.

2. Background and Related Art

Orthopedic surgeons are experiencing a proliferation of knee replacementsurgeries. The demand appears driven by the fact that few proceduresreturn as much quality of life as joint replacement.

Moreover, the increased need for knee replacements implicates the needfor durable and long lasting artificial knee devices that provide forand allow full, functional flexion. That is, there is a great need forresearch that provides new medical advances on the overall function andperformance of knee prostheses, and improves corresponding surgicalmaterials and technologies related to such devices.

Improvements to knee prostheses correspondingly increase with demand.Thus, currently-available knee prostheses mimic characteristics of thenormal knee more than those previously used. Unfortunately, today's kneeprostheses still have many shortcomings.

Among the shortcomings is the inability of a knee prosthesis patient toachieve deep knee flexion, also known as full functional flexion. Thoughsome currently available knee prostheses allow for knee flexion (i.e.,bending) of more than 130 degrees from full limb extension (zero degreesbeing when the patient's knee is fully extended and straight); suchprostheses and results are uncommon. Full functional or deep kneeflexion is where the limb is bent to its maximum extent, which may bewith the femur and tibia at an angle to each other of 140 degrees ormore, though the actual angle varies from person to person and with bodyhabitus. Full extension is where the leg/limb is straight and the personis in a standing position.

To illustrate the average range in degrees achieved by patients havingstandard knee prostheses, the following is provided. When a patient'sknee or limb is fully extended, the femur and tibia are in the sameplane—at zero degrees or up to 5-10 degrees of hyperextension in someindividuals. However, once the knee bends, and the distal tibia movestoward the buttocks, the angle increases from zero to 90 degrees for aperson sitting in a chair. Furthermore, when the tibia is closest to thefemur, and the heel is almost at, if not touching, the buttock, theangle is around 160 degrees or more. Most knee prosthesis patients areunable to achieve the latter position or any position placing the kneejoint at angles above 130 degrees.

For many people, such a limb and body position is not often achieved ordesired most of the time. However, nearly everyone, at some point intime, whether or not it occurs when a person is getting on and off theground to play with children, or merely incidental to those livingactive lifestyles, finds themselves in a position requiring knee flexiongreater than 130 degrees. Unfortunately, those with currently-availableknee prostheses are unable to participate in any activity requiringgreater knee flexion and are thus limited to watching from thesidelines.

In many populations and cultures such a limb/knee and body position isdesired and necessary the majority of the time. For instance, in Asianand Indian cultures, full functional flexion and the squatting positionis common and performed for relatively long periods of time.

A need, therefore, exists for knee prostheses for those patients andespecially for those in cultures where extensive squatting, sitting withknees fully flexed, and/or kneeling when praying or eating is common, toachieve knee flexion greater than presently possible among those whohave currently-available knee prostheses.

Thus, while techniques currently exist that relate to knee prostheses,challenges still exist. Accordingly, it would be an improvement in theart to augment or even replace current techniques with other techniques.

SUMMARY OF THE INVENTION

The present invention relates to knee prostheses. In particular, thepresent invention relates to systems and methods for providing deeperknee flexion capabilities for knee prosthesis patients, and moreparticularly, to: (i) providing a greater articular surface area to thefemoral component of a knee prosthesis, with either a modification of,or an attachment to the femoral component of a knee prosthesis, whichwhen integrated with a patient's femur and an appropriate tibialcomponent, results in full functional flexion; (ii) providingmodifications to the internal geometry of the femoral component and theopposing femoral bone with methods of implanting; (iii) providingasymmetrical under surfaces on the tibial component of the kneeprosthesis and uniquely-positioned articular surfaces to facilitate fullfunctional flexion; and (iv) asymmetrical femoral condylar surfaces witha lateralized patellar (trochlear) groove to more closely replicatephysiologic loading of the knee and to provide better tracking of thepatella.

In a normal knee, there is a cessation of active flexion atapproximately 120°, first, because the hamstring muscles lose theirmechanical advantage, and secondly because the medial femoral condylerolls posteriorly which does not occur up to 120°. By 120° of flexion,the medial femoral condyle starts to roll backwards relative to theposterior horn of the medial meniscus of the tibia. At 140° of flexion,the femur moves up on to the posterior horn of the medial meniscus.Accordingly, resistance to flexion is felt at this point and beyond. Byfull flexion, the medial femoral condyle has moved back approximately 8mm from its position at 120° to a position 10 mm from the posteriortibial cortex. Laterally, the femur moves back an additional 5 mm inhyperflexion so that there is little or no tibiofemoral rotation between120° and 160°. Accordingly, the hyperflexion between 120° and 160° is aseparate arc than the kinematics from 0° to 120° of flexion, and at160°, the posterior horn of the lateral meniscus comes to lie on theposterior surface of the tibia distal to the femoral condyle. As such,the posterior horn is not compressed and the two bones are in directcontact.

The final limit to hyperflexion arises because the posterior horn of themedial meniscus impedes flexion at 140° and limits it absolutely at160°. The posterior horn also prevents the medial femoral condyle frommoving back beyond a point 10 mm from the posterior tibial cortex. Thus,the posterior horn of the medial meniscus is a key structure inachieving deep flexion.

Implementation of the present invention takes place in association withimproved knee prostheses that enable knee prosthesis patients to achievegreater deep knee flexion than previously achievable usingpresently-designed knee prostheses. In at least some implementations ofthe present invention, greater deep knee flexion is provided to the kneeprosthesis by resecting portions of the femur to allow additionalclearance for the posterior horn of the medial meniscus. At least someimplementations of the present invention further provide positioningand/or installing an articular surface within resectioned portions ofthe femur to provide an interface between the posterior horn of themedial meniscus and the resectioned surface of the femur.

In at least some implementations of the present invention, greater deepknee flexion is provided to the knee prosthesis by providing anarticular surface on the proximal, anterior surface (or portion) of theposterior condyles of the femur. At least some implementations of thepresent invention embrace an additional or increased articular surfaceon the proximal, anterior portion of either or both of the medial orlateral posterior condyles of the femoral component of the prosthesis.Embodiments of the femoral component add increased articular surfacearea to the proximal end of the posterior condyles of the femoralcomponent in an anterior direction such that when the patient bends hisor her knee during deep knee flexion, contact between the femoralcomponent and the tibial component is maintained, and a greater, deeperknee flexion can be achieved.

In at least some implementations of the present invention, greater deepknee flexion can be provided or improved by modifying the tibialarticulation, in which the center of the conforming medial tibialarticular surface of the tibial component of the prosthesis is movedposterior relative to what is currently available. Additionally, in somesuch embodiments, the overall shape of the lateral tibial articularsurface is modified.

In at least some implementations of the present invention, greater deepknee flexion can be achieved by providing an asymmetrical femoralcomponent of the prosthesis. The asymmetrical femoral component permitstransfer of more than one-half of the force transmitted across the jointto be transmitted to the medial side, as occurs in the normal knee. Insome implementations, other modifications to the tibial and femoralcomponents of a knee prosthesis may be made, including having asymmetricfemoral condyles, having a closing radius on the femoral component, andremoving certain areas of the tibial and femoral components; wherein allof the foregoing result in deeper knee flexion capabilities for kneeprosthesis patients than previously achievable.

While the methods, modifications and components of the present inventionhave proven to be particularly useful in the area of knee prostheses,those skilled in the art will appreciate that the methods, modificationsand components can be used in a variety of different orthopedic andmedical applications.

These and other features and advantages of the present invention will beset forth or will become more fully apparent in the description thatfollows and in the appended claims. The features and advantages may berealized and obtained by means of the instruments and combinationsparticularly pointed out in the appended claims. Furthermore, thefeatures and advantages of the invention may be learned by the practiceof the invention or will be obvious from the description, as set forthhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the manner in which the above recited and other featuresand advantages of the present invention are obtained, a more particulardescription of the invention will be rendered by reference to specificembodiments thereof, which are illustrated in the appended drawings.Understanding that the drawings depict only typical embodiments of thepresent invention and are not, therefore, to be considered as limitingthe scope of the invention, the present invention will be described andexplained with additional specificity and detail through the use of theaccompanying drawings in which:

FIGS. 1A and 1B depict ranges of flexion of a knee joint;

FIGS. 2A-2C and 3A-3C depict various views of a generic knee prosthesis;

FIGS. 4A-4D depict representative perspective views of embodiments of afemoral component of a knee prosthesis in accordance with embodiments ofthe present invention;

FIGS. 5A-5D depict representative perspective views of embodiments of afemoral component of a knee prosthesis in accordance with embodiments ofthe present invention;

FIGS. 6A-6B depict side views of a representative prior art tibialcomponent of a knee prosthesis;

FIGS. 6C-6D depict side views of a representative embodiment of a tibialcomponent in accordance with embodiments of the present invention;

FIGS. 6E-6F depict an alternate embodiment of a representative tibialcomponent modified to include a raised ridge articulation feature.

FIGS. 6G-6H depict an alternate embodiment of a representative tibialcomponent modified to include a spherical articulation feature.

FIGS. 7A and 7B depict alternate embodiments of femoral and tibialcomponents in accordance with embodiments of the present invention;

FIG. 8A illustrates a conventional femoral component while FIG. 8Billustrates an embodiment of a femoral component in accordance with thepresent invention;

FIG. 9 illustrates a modular attachment for use with embodiments of afemoral component in accordance with embodiments of the presentinvention;

FIGS. 10A-10H illustrate representative steps for attaching anembodiment of a femoral component to a femur, the resectioned portionsof the femur shown in phantom;

FIGS. 11A-11K illustrate representative steps for attaching an alternateembodiment of a femoral component to a femur;

FIGS. 12A-12B and FIG. 13 illustrate comparisons between a conventionalfemoral component and an embodiment of a femoral component in accordancewith embodiments of the present invention;

FIG. 14 illustrates an alternate embodiment of a femoral component inaccordance with embodiments of the present invention;

FIGS. 15A-15D illustrate comparisons between embodiments of a femoralcomponent;

FIGS. 16A-16D illustrate a manner in which an articulating surface ofthe femoral components shown in FIGS. 15A-15D may be extended;

FIG. 16E illustrates a shortened embodiment in which an articulatingsurface of the femoral component may be extended;

FIG. 16F illustrates a unicompartmental femoral component including anextended articulating surface in accordance with a representativeembodiment of the present invention;

FIG. 17 illustrates a radiograph of a normal knee flexed toapproximately 160 degrees, and further illustrating the position of thepatella;

FIG. 18 illustrates an alternate embodiment of a femoral component;

FIG. 19A illustrates a tibial component that does not have an articularsurface posterior to the main articular surface;

FIG. 19B illustrates the Tibial Full Flex articulation being posteriorto the main weight bearing articulation;

FIGS. 20A-20I illustrate a representative interaction of the FemoralFull Flex articulation and the Tibial Full Flex articulation;

FIG. 21 illustrates a representative interaction of the posteriorarticulate surface of the medial plateau of the tibia and the poplitealsurface during deep flexion of the knee;

FIG. 22 illustrates a representative implementation of a resection blockand the femur following resection of the popliteal surface;

FIG. 22A illustrates a representative implementation of a resectionblock and the femur prior to resection of the popliteal surface;

FIG. 23 illustrates a representative interaction of the posteriorarticulate surface of the medial plateau of the tibia and an extendedportion of the femoral component of the knee prosthesis during deepflexion; and

FIG. 23A illustrates a representative interaction of the posterior fullflex articular surface of the medial tibial plateau of a tibialcomponent and an extended portion of the femoral component of the kneeprosthesis during deep flexion.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to knee prostheses. In particular, thepresent invention relates to systems and methods for providing deeperknee flexion capabilities for knee prosthesis patients, and moreparticularly, to: (i) providing an extended articular surface on theproximal, anterior surface (or portion) of the posterior condyles of thefemur; (ii) making modifications to the internal geometry of the femoralcomponent and the associated femoral bone cuts with methods ofimplantation; (iii) making modifications to the tibial and femoralcomponents of a knee prosthesis, including asymmetrical tibial articularsurfaces and removing certain areas of the tibial and femoralcomponents; and (iv) having asymmetric femoral condyles, includinghaving a closing radius on the femoral component, wherein all of theforegoing result in deeper knee flexion capabilities for knee prosthesispatients than previously achievable.

It is emphasized that the present invention, as illustrated in thefigures and description herein, may be embodied in other forms. Thus,neither the drawings nor the following more detailed description of thevarious embodiments of the system and method of the present inventionlimit the scope of the invention. The drawings and detailed descriptionare merely representative of examples of embodiments of the invention;the substantive scope of the present invention is limited only by theappended claims recited to describe the many embodiments. The variousembodiments of the invention will best be understood by reference to thedrawings, wherein like elements are designated by like alphanumericcharacter throughout.

With reference now to the accompanying drawings, FIGS. 1A-3C areprovided for general reference to assist in understanding the featuresof the embodiments of the present invention. FIGS. 1A and 1B depict arange of angles possible between the tibia and femur in a person who isextending and flexing (bending) his or her knee. Specifically, FIG. 1Adepicts a range of angles possible while the person extends and bendshis or her knee, realizing that some knees may flex to 160 degrees, 165degrees, or beyond. FIG. 1B depicts these various angles in analternative position. These figures should be kept in mind during thediscussion illustrating how with the embodiments of the presentinvention, knee flexion of greater than 135 degrees is possible for kneeprosthetic patients, which is not generally possible withcurrently-available knee prostheses.

FIGS. 2A-2C depict various perspective views of a generic kneeprosthesis 10. Specifically, FIG. 2A depicts a sagittal view of a leftknee joint having a knee joint prosthesis 10, with the tibia and thefemur of the normal knee transparent. FIG. 2B depicts an enlarged viewof a femoral component 12 of the knee prosthesis 10, while FIG. 2Cprovides a top perspective view of a tibial component 14 of the kneeprosthesis. FIG. 2B depicts certain components of the femoral component12, such a medial receiving area 16 that may be modified in embodimentsof the present invention to integrally connect with an attachment (notshown but hereinafter described) as well as a lateral receiving area 18.The internal geometry of the femoral component 12 is provided to allow aone piece femoral component 12 that is rolled into place on theresectioned femur 32, as shown in FIG. 4D. Thus, the internal geometryof the femoral component 12 includes various surfaces, including areas16 and 18, to accommodate the patellar articulation and the anteriorextensions of the proximal portions of the posterior condyles. Theresectioned portions of the condyles provide flat surfaces which areloaded in compression in full knee flexion. Additionally, theresectioned surfaces are provided such that the articular surface of thefemoral component is at essentially the same position as the surfacebeing resectioned. As such, the normal relationship between the femurand the tibia is preserved with full flexion. Additionally, when theknee is fully flexed, the interface between the femoral component andthe underlying femur is mainly loaded in compression rather than sheerforces. Compression forces provide a more stable interface between thefemoral component and the femur thereby decreasing the chances ofloosening. Therefore, in some embodiments the interface between thefemoral component and the tibial component are configured to enhance acompression force between the femoral component and the underlying femurduring full flexion of the knee joint.

Also visible in FIG. 2B is a medial femoral condylar surface 20 and alateral femoral condylar surface 22. FIG. 2C depicts the tibialcomponent 14 and its elements: a lateral tibial condylar surface 24, amedial tibial condylar surface 26, and an intercondylar surface 28. Whenthe knee prosthesis 10 is functioning, an interface exists between themedial femoral condylar surface 20 of the femoral component 12 and themedial tibial condylar surface 26 of the tibial component 14 and betweenthe lateral femoral condylar surface 22 of the femoral component 12 andthe lateral tibial condylar surface 24 of the tibial component 14.

FIGS. 3A-3C depict additional perspective views of the generic kneeprosthesis 10 with its different components. Specifically, FIG. 3Adepicts a frontal view of the knee prosthesis 10 with the femoralcomponent 12 articulating with the tibial component 14 as describedabove. FIG. 3B is a side view of the femoral component 12, and FIG. 3Cis a side view of the tibial component 14, and specifically, of themedial side of the tibial component showing the medial tibial condylarsurface 26. The medial femoral condylar surface 20 slidingly interfaceswith the medial tibial condylar surface 26 so that as a person flexes orextends his or her knee, the arc of the medial femoral condylar surface20 runs along the media tibial condylar surface 26.

In some embodiments of the present invention, greater deep knee flexionis provided to the knee prosthesis 10 by providing an articular surfaceon the proximal, anterior surface (or portion) of the posterior condylesof the femur. At least some embodiments of the present invention embracean additional or increased articular surface on the proximal, anteriorportion of either or both of the medial or lateral posterior condyles ofthe femoral component 12. Embodiments of the femoral component 12 addincreased articular surface area to the proximal end of the posteriorcondyles of the femoral component 12 in an anterior direction such thatwhen the patient bends his or her knee during deep knee flexion, contactbetween the femoral component 12 and the tibial component 14 ismaintained, and a greater, deeper knee flexion can be achieved.

Four different examples of how this may be achieved are demonstratedwith reference to the Figures. Any method of increasing an articularsurface area to the proximal end of the posterior condyles of thefemoral component 12 in an anterior direction is embraced by theembodiments of the present invention.

FIGS. 8A and 8B illustrate a femoral component 12 and method ofincreasing an articular surface area to the proximal end of theposterior condyles of the femoral component 12. FIG. 8A illustrates aside view of a conventional femoral component 12. In the firstembodiment of the inventive prosthesis, the shaded area of the femoralcomponent 12 of FIG. 8A, i.e. the posterior condyle, is thickened in theanterior direction until the resulting surface opposing the bone isapproaching the same plane as the posterior surface of the shaft of thedistal femur. This thickening may be seen with reference to FIG. 8B.This results in a greater articular surface area of the posteriorcondyles of the femoral component 12. This requires resection of morebone but is otherwise an easy modification to current prostheses andrequires little to no modification of current surgical technique.

A second type of embodiment that extends the articular surface area isillustrated by FIGS. 4A-5C. Methods of utilizing this type of embodimentare illustrated with reference to FIGS. 9-10H. This type of embodimentutilizes an extension attachment to the femoral component 12 of anembodiment of the knee prosthesis 10, which when integrated with boththe femoral component 12 and a patient's femur, results in a greatersurface area of the femoral component 12.

As illustrated in FIGS. 4A-5D, this type of embodiment has a modularattachment 30 that provides a modular flexion attachment surface toextend the articular surface area of the anterior portion of theproximal portion of the posterior condyles. The modular attachment 30may be attached to the inside, or non-articular surface, of a relativelyconventional total knee femoral component 12. The modular attachment 30has a portion that may be partially received, in one embodiment, withina recessed receiving area on the flat anterior surface of one or both ofthe posterior condyles of the femoral component 12 and may thus be usedon the medial posterior condyle, the lateral posterior condyle, or both.Alternatively, it may be implanted in a groove within either or both ofthe resected posterior condyles of the femur itself.

The modular attachment 30 provides an increased articular contact areaas an anterior continuation of the medial femoral condylar surface 20and/or of the lateral femoral condylar surface 22 of the femoralcomponent 12. In some embodiments, the modular attachment 30 may beinitially placed onto the femoral component 12 and then attached to thedistal end of the patient's femur. In other embodiments, the modularattachment 30 may be connected first to the posterior condyles of thedistal end of the femur and then integrally connected with the femoralcomponent 12. The modular attachment 30 may be used on the medial side,on the lateral side or on both sides.

FIGS. 4A-4D depict perspective views of embodiments of the femoralcomponent 12 and the modular attachment 30. As described, the modularattachment 30 attaches to the femoral component 12 and to the femur of apatient to enlarge the surface area of the femoral component 12 and,ultimately, to enable deep knee flexion beyond 140 degrees in a kneeprosthesis patient. FIG. 4A depicts a simplified side view of anembodiment of the femoral component 12 having the modular attachment 30attached to the posterior condyle of the femoral component. FIG. 4Ddepicts a side view of the attachment integrally attached to a patient'sfemur and to the femoral component of the knee prosthesis. The modularattachment 30 may be modular as shown in FIGS. 4B-4D and may fit withina recess in either or both of the medial receiving area 16 and thelateral receiving area 18 (i.e. in the anterior interior surface of theposterior condyles of the femoral component 12, as shown in FIG. 2B)and/or in either or both of the medial and the lateral posteriorcondyles of the femur or in both the femoral component 12 and the femur.In another embodiment the modular attachment 30 may be a permanent partof the femoral component, as discussed below.

FIG. 4B depicts a side view of one embodiment the modular attachment 30and FIG. 4C depicts a top view of the depicted embodiment of the modularattachment 30. Specific dimensions of the depicted embodiment of themodular attachment 30 are not given and one of skill in the art willrecognize that the dimensions may be modified from patient to patientand will also recognize that the various portions of the modularattachment 30 may all be formed in some embodiments to be as wide as thecondyle of the femoral component 12.

In some embodiments, the modular attachment 30 includes a first portionroughly perpendicular to a second portion. The first portion of themodular attachment 30 entails a flanged articular area 36 (“flanged area36”) at one end of the modular attachment 30, and an elongated stem 38extending therefrom, which extends roughly perpendicular from theflanged area, distally from the flanged area 36. The elongated stem 38therefore is attached to the non-articular side of the flanged area 36.Although the elongated stem is illustrated in FIG. 4C as having amedial-lateral width substantially shorter than the medial-lateral widthof the flanged area 36, the elongated stem 38 of other embodiments maybe of any medial-lateral width up to the medial-lateral width of theposterior condyles of the femoral component 12 itself.

The elongated stem 38 has an upper side 40 and a lower side 42. Nodules44 may be placed on either or both of the upper side 40 and the lowerside 42, to enable an integral connection with the femur 32 on the upperside 40, and the femoral component 12 on the lower side 42. Some form ofa nodule-receiving groove or recess (not shown) may be made in the femur32 and/or the femoral component 12 to receive these nodules 44 and tosecure the integral connection between the femur 32, the attachment 30,and the femoral component 12; with the modular attachment 30 beingdisposed between the femur 32 and the femoral component 12.

In embodiments having no nodules 44 on the elongated stem 38, theattachment 30 may fit within a recess made on either or both of themedial receiving area 16 and the lateral receiving area 18 of thefemoral component 12. The elongated stem 38 of the modular attachment 30would fit within such recesses and integrally connect thereto. Themodular attachment 30 may simultaneously connect with the femur 32 onthe upper side 40 (generally) of the elongated stem 38. In embodimentshaving no nodules on the elongated stem, the stem of the modular portionmay further fit into a groove prepared in the resected posteriorcondyles of the femur.

The modular attachment 30 increases the overall surface area of thefemoral component 12 and prolongs the interface and contact that existsbetween the femoral component 12 and the tibial component 14. Thisenables greater knee flexion in prosthetic knee patients because thefemoral component 12 remains interfaced with the tibial component 14throughout the full range of flexion resulting in pain-free kneeflexion.

Without this increased surface area, the medial and lateral proximaledges of the posterior femoral condyles of a prothesis may push into theproximal surfaces of the tibial component 14 and may produce wear of thetibial component 14. In addition, the tibial component 14 may contactthe bone of the distal femur 32 that is anterior and/or proximal to theproximal edges of the posterior condyles of the prosthesis and causepain to and limit flexion of the prosthetic knee patient and may causewear to the tibial component. Further, without this added surface area,with flexion beyond 140 degrees, the tibial component 14 may exert aforce in the distal direction on the femoral component 12, which mayresult in loosening of the femoral component 12. Therefore, the modularattachment 30 extends the life of the prosthetic knee, decreases pain tothe patient, and ultimately, enables a prosthetic knee patient toachieve deep knee or full functional flexion.

FIGS. 5A-5D depict various perspective views of the modular attachment30 as it is attached to the femoral component 12 and to the femur 32.FIG. 5A is illustrative of the modular attachment 30 as it is attachedto the femur 32 prior to attachment of the femoral component 12. FIGS.5B-5D are illustrative of the modular attachment 30 as it is recessedwithin the femoral component 12 prior to attachment to the femur 32, andspecifically, as the modular attachment 30 is integrally connected toeither or both of the medial femoral receiving area 16 and the lateralfemoral receiving areas 18.

FIG. 9 and FIGS. 10A-10H illustrate methods of attaching the modularattachment 30 to the femur 32, followed by attaching the femoralcomponent 12 to the femur 32 and modular attachment 30. FIG. 9illustrates the resection needed on the femur 32 prior to creating therecess in the femur to allow attaching the modular attachment 30. FIG. 9and FIGS. 10A-10H do not illustrate the specific resection needed forthe modular attachment 30, but the resection needed will be appreciatedby one of skill in the art. After resection is completed, as at FIG.10A, the modular attachment 30 may be attached to the femur as at FIG.10B. The femoral component 12 may then be attached to the femur 32 (andto the modular attachment 30, if desired) by positioning and moving thefemoral component 12 as illustrated in FIGS. 10C-10H. As may beappreciated from the sequence of illustrations depicted in FIGS.10C-10H, the femoral component 12 needs to be rotated or rolled intoposition, with initial contact beginning in the posterior region asillustrated in FIG. 10E and progressing to the fully-seated positionillustrated in FIG. 10G. This is a new implantation technique that willrequire some additional practice and training over current techniques.

As has been set forth above in reference to FIG. 4A, a third type ofembodiment having an extended articular surface is not modular and doesnot utilize a separate modular attachment 30. In such embodiments, anextended articular surface corresponding to the flanged area 36 of themodular attachment 30 may be integrally formed as part of one or bothcondyles of the femoral component 12. Placement of one such embodimentis illustrated with reference to FIGS. 11A-11K. As may be appreciatedwith reference to these Figures, placement of such an embodiment alsoutilizes a similar rotational placement technique to that illustrated inFIGS. 10C-10H. As may be appreciated by reference to FIGS. 10H and 11K,any of the modular or non-modular embodiments may, optionally, befurther secured by one or more screws placed in an anterior flange ofthe femoral component 12.

One advantage of the embodiment illustrated in FIGS. 11A-11K is that theimplanting surgeon may decide whether to utilize the illustratedembodiment or a traditional femoral component 12 after the distal andanterior oblique cuts have been made. This is illustrated in FIGS. 12Aand 12B. FIG. 12A shows a traditional femoral component 12. FIG. 12Bshows the embodiment of the femoral component 12 illustrated in FIGS.11A-11K. As may be appreciated by reference to the Figures, the distalcuts 62 and anterior oblique cuts 64 are essentially identical. This maybe further appreciated by reference to FIG. 13, which shows asuperimposed view of FIGS. 12A and 12B, not only showing that the distalfemoral cuts 62 and the anterior oblique cuts 64 are identical, but alsoshowing that the total amount of bone resected for the illustratedembodiment is similar to or less than the amount resected using currenttechniques and femoral components 12.

In a non-modular embodiment of the femoral component 12 as shown inFIGS. 11A-11K and in a modular embodiment of the femoral component asshown in FIGS. 4A-5D, there are junctions where the inside flat surfacesof the prosthesis (which when implanted are in contact with the bone)meet. These flat surfaces, rather than coming together at a sharp angle,may or may not have a radius connecting the two flat surfaces. Not allof the junctions of the flat surfaces necessarily need a radius and insome embodiments none of the junctions of flat surfaces will have radii.The flat surfaces may or may not be in exactly the same planes as onconventional knees and will provide for the placement of a non-modularsurface that will provide an articulation for the proximal, anteriorportion of the posterior femoral condyles extending to or almost to aplane that is a continuation of the posterior cortex of the distalfemoral shaft. In embodiments where one or more radii are provided tothe junction(s) of the inside flat surfaces of the femoral component 12,corresponding radii 31 or curvatures may be provided to the resectedbone surface of the femur, as is illustrated in FIG. 5A. As may beappreciated by one of skill in the art, the presence of thecorresponding radii 31 may assist in the rotational placement of thefemoral component 12 as illustrated in FIGS. 10A-10H and 11A-11K.

This internal configuration allows the femoral component 12 to beinitially applied to the femur in a flexed position and then rotatedinto the fully extended position as it is implanted fully, asillustrated and discussed with reference to FIGS. 10A-10H and 11A-11K.Screw(s) may, optionally, be placed in the anterior flange of thefemoral component 12 to firmly stabilize the component. This abilityfacilitates implanting the non-modular femoral component 12 or a modularfemoral component 12 with the modular attachment 30 already implanted onthe posterior condyles of the femur 32.

A fourth type of embodiment of the femoral component 12 is illustratedin FIG. 14. This type of embodiment has a femoral component 12 thatreplaces the weight-bearing distal femoral condyles, in addition to someor all of the articular surface of the posterior condyles extendingproximally and anteriorly to an area that is in the same plane as acontinuation of the posterior cortex of the distal one fourth to onethird of the femur. Such an embodiment may comprise separate medial andlateral components or they may be attached together to form onecomponent that replaces or resurfaces the medial and lateral condyles.

Historically, many early total knee femoral components 12 did nothingregarding the patello-femoral joint. Because a certain percentage ofthose patients had anterior knee pain, an anterior flange was added tothe femoral component 12 to resurface the trochlea (patellar groove).This weakened the patella and resulted in fractures in some patients.Recently techniques have been developed to minimize patellar pain whichdo not require implantation of a component. The embodiment shown in FIG.14 does not have an anterior flange that is an integral part on thecondylar portion of the prosthesis. It is anticipated that such a devicealone may, in some patients, be adequate to replace the femoral condylesand allow the surgeon to treat the patello-femoral joint as he/she feltwas indicated. Alternatively, a separate patello-femoral articularsurface or surfaces could be implanted. The patello-femoral implant(s)could be entirely separate or could be modular and attached to thedevice shown in FIG. 14. The embodiment illustrated in FIG. 14 includesthe ability to attach a modular anterior flange (trochlear groove) tothe device shown in the Figure. It can be appreciated in FIG. 14 thatthe prosthesis shown with the profile of the femur in light outline,could not be implanted without significant flexion of the knee.

Implementations of the present invention embrace a femoral component 12,a tibial component 14 and/or a modular attachment 30 each comprise ametal, metal alloy, ceramic, carbon fiber, glass, polymer (includingbone cement), organic material, retrieved human or animal tissue, andnaturally occurring or synthetic materials used either separately or inany combination of two or more of the materials.

As may be appreciated by reference to the above discussion and thecorresponding Figures, currently-existing femoral components 12 providean articular surface that only extends a short distance in the proximalanterior direction of the posterior condyle. For example, as may be seenwith reference to FIGS. 2A and 8A, the articular surface at the anteriorend of the posterior condyle typically extends to and replaces at mostthe posterior third of the posterior condyle, as measured from the mostposterior portion of the patient's original posterior condyle (or fromthe most posterior portion of the femoral component 12) to a plane thatis a continuation of the distal one fourth to one third of the posteriorcortex of the femoral shaft.

In contrast, the various embodiments of the femoral component 12illustrated in the Figures and discussed above provide an extendedarticular surface for either or both of the medial condyle and thelateral condyle that extends in a proximal anterior direction so as toextend half or more of the anteroposterior distance between the mostposterior portion of the posterior condyle and the plane that is acontinuation of the distal one fourth to one third of the posteriorcortex of the femoral shaft. In some embodiments, the extended articularsurface extends at least two-thirds of the anteroposterior distancebetween the most posterior portion of the posterior condyle and theplane that is a continuation of the distal one fourth to one third ofthe posterior cortex of the femoral shaft. In other embodiments, theextended articular surface extends nearly the entire anteroposteriordistance between the most posterior portion of the posterior condyle andthe plane that is a continuation of the distal one fourth to one thirdof the posterior cortex of the femoral shaft. In still otherembodiments, the extended articular surface may extend even further, toencompass a distal portion of the posterior cortex of the femoral shaft,as illustrated in FIGS. 16A-16D.

The surface of the extension, which may or may not contact bone and is acontinuation of the femoral articular surface, can be referred to as theFull Flex Articulation. There may be a corresponding surface on theposterior edge of the medial and or lateral_tibial articulation which isnot part of the articular surface of the tibia when the tibia is in fullextension. For example, in some implementations of the current inventionthere is a corresponding surface on the posterior edge of the medialtibial articulation where the center of the medial articular surface ismore than 20% of the distance from the posterior edge of the componentto the anterior edge.

The embodiment illustrated in FIG. 19A shows a non-articular surface 41posterior to the main articular surface 43. FIG. 19B illustrates a fullflex articular surface 45 and an articular surface 47. The Tibial FullFlex articulation of FIG. 19B is posterior to the main weight bearingarticulation and articulates with a specific articular area on thefemoral component, the Femoral Full Flex articulation (proximalextension 50) shown in FIGS. 16A-16D and shown in a slightly shortenedembodiment in FIG. 16E.

With reference to FIG. 16F, a representative embodiment of aunicompartmental femoral component 120 is shown. The various componentsof the present invention may be substituted with a unicompartmentalcomponent, as discussed below. The unicompartmental component isgenerally implanted to replace the weight bearing portion of the kneejoint medially or laterally. The unicompartmental component may be usedmedially or laterally as two separate femoral and two separate tibialcomponents on just the weight bearing portion of the joint. In someembodiments, the unicompartmental component is used with two femoral ortwo tibial components joined, but ignoring the patello-femoral joint. Inother embodiments, the unicompartmental component is used as one femoralcomponent replacing the medial and lateral weight bearing portions ofthe distal femur and also the patello-femoral joint with either a onepiece tibial component or separate medial and lateral tibial components.Finally, in some embodiments the unicompartmental component is aone-piece, femoral component replacing the patello-femoral joint andeither the medial or lateral weight-bearing portion of the femur.

In some embodiments, the unicompartmental component 120 includes a FullFlex Femoral articulation surface 50. As previously discussed, thearticulation surface 50 is configured to provide extended contactbetween the unicompartmental femoral component 120 and a Full FlexTibial articulation surface 55 of a tibial component during deep flexionof the knee. In some embodiments, a portion of the popliteal surface 202of the femur is removed to accept placement of the articulation surface50. In other embodiments, a unicompartmental component (not shown) isprovided for use in conjunction with a modular Full Flex Femoralarticulation surface (not shown). Thus, in some embodiments a firstportion of the femur is prepared to receive the unicompartmentalcomponent 120, and a second portion of the femur is prepared to receivea modular Full Flex Femoral articulation surface (not shown). As such, acombination of the unicompartmental component and the modular Full FlexFemoral articulation surface provide a unicompartmental femoralcomponent that is functionally equivalent to the unicompartmentalfemoral component 120.

In some embodiments, the unicompartmental femoral component 120 is usedin conjunction with a unicompartmental tibial component. In otherembodiments, the unicompartmental femoral component 120 is used inconjunction with a full tibial component. Finally, in some embodiments,the unicompartmental femoral component 120 is used directly inconjunction with a natural surface of the opposing tibia.

Where permitted, implementation of a unicompartmental femoral component120 provides several advantages over total knee replacement procedures.For example, while an eight-inch incision is typically required for atotal knee replacement surgery, a partial knee replacement utilizing aunicompartmental femoral component 120 requires an incision ofapproximately three-inches. Thus, one benefit of a unicompartmentalfemoral component 120 is decreased scarring following the partial kneereplacement procedure.

Other benefits of a partial knee replacement include decreased recoverytime, increase range of motion, and decreased overall damage to theknee. A total knee replacement procedure may require the patient toremain in the hospital for up to four days. It can also take up to threemonths, or longer, to recover from the surgery. However, with a partialknee replacement procedure, a patient typically requires no more thantwo days of hospitalization followed by one month of recovery.Additionally, a patient is typically able to walk without assistance aweek or two following the partial knee replacement procedure.

Unlike some total knee replacement procedures, insertion of theunicompartmental femoral component 120 generally preserves moreligaments thereby providing a fuller range of motion. For example, insome partial knee replacement procedures, the anterior and/or posteriorcruciate ligaments are preserved, as desired. A partial knee replacementalso generally results in less damage to the knee because the surgery isminimally invasive thereby causing minimal tissue, muscle and tendondamage to the knee.

For some partial knee replacement procedures, various methods may beimplemented to address pain and discomfort caused by patello-femoralarthritis. For example, for some partial knee replacement proceduresdenervation of the patella is performed. In other partial kneereplacement procedures, denervation of the opposing femoral groove isperformed. In some embodiments of the present invention theunicompartmental femoral component 120 is designed to reproduce thenatural patello-femoral joint throughout the range of motion and tofacilitate tracking of the patella in the femoral groove. In otherembodiments, a combination of denervation and natural design of theunicompartmental femoral component 120 are implemented to adequatelyaddress the patello-femoral arthritis.

The interaction of the Femoral Full Flex articulation 50 and the TibialFull Flex articulation 55 is illustrated in FIGS. 20A-20I, wherein FIGS.20A-20E are at 0 degrees, FIGS. 20E-20 is at 90 degrees, FIG. 20G is at130 degrees, FIG. 20H is at 150 degrees, and FIG. 20I is at 160+degrees. FIG. 20B identifies a representative position of unresectedtibial plateau 51. FIG. 20C identifies a representative closing radiuson a posterior portion of a femoral component 53. FIG. 20D identifies arepresentative Full Flex Femoral articulation 50. FIG. 20E identifies arepresentative Full Flex Tibial articulation 55. FIG. 20H identifies arepresentative approach of the Full Flex Femoral articulation 50 to theFull Flex Tibial articulation 55 during flexion. FIG. 20I identifies arepresentative contact of the Full Flex Femoral articulation 50 to theFull Flex Tibial articulation 55 during deep flexion.

FIGS. 15A-15D illustrate the various manners in which the fourpreviously-discussed embodiments of the femoral component 12 provide anextended articular surface 48. The concept of adding more articularsurface to the proximal portion of the posterior condyles of the femoralcomponent may be generally accomplished by extending the proximalportion anteriorly until the articular surface approaches, or extendsbeyond the plane of the posterior surface of the shaft of the distalfemur, if that plane were to extend distally. For example, as may beseen from FIGS. 15A-15D, the extended articular surface 48 of eachembodiment extends the articular surface at the anterior end of one orboth of the medial posterior condyle or the lateral posterior condyle.As illustrated in FIGS. 16A-16D, the articular surface may be furtherextended in a proximal direction from the end of the extended articularsurface 48. This further extension may be provided by a proximalextension 50. The proximal extension 50 may be an integral part of thefemoral component 12, it may be a part of the modular attachment 30, orit may be provided as a separate and additional component. In oneembodiments where the proximal extension 50 is provided, the proximalextension 50 acts as a fulcrum that interacts with the tibia or with thetibial component 14 to increase separation between the femur 32 and thetibia during full functional flexion to improve the deep knee flexion.In another embodiment, the proximal extension 50 allows the normalrelationships between the tibia and femur in full functional flexion toexist while maintaining contact between the two surfaces.

Thus, in some embodiments of the present invention, greater deep kneeflexion is facilitated by providing an articular surface on theproximal, anterior surface (or portion) of the posterior condyles of thefemur. At least some such embodiments embrace an additional or increasedarticular surface on the proximal, anterior portion of either or both ofthe medial or lateral posterior condyles of the femoral component 12.Embodiments of the femoral component 12 add increased articular surfacearea to the proximal end of the posterior condyles of the femoralcomponent 12 in an anterior direction such that when the patient bendshis or her knee during deep knee or full functional flexion, contactbetween the femoral component 12 and the tibial component 14 ismaintained, and a greater, deeper knee flexion may be achieved.

In at least some embodiments of the present invention, greater deep kneeflexion may be provided or improved by modifying the tibialarticulation, in which the center of the conforming medial tibialarticular surface of the tibial component 14 is moved posterior relativeto what is currently available. Additionally, in some such embodiments,the overall shape of the lateral tibial articular surface may bemodified. This is illustrated with reference to FIGS. 6A-6D.

In such embodiments of the tibial component 14, the condylar orarticular plateau surfaces may be asymmetric. That is, the lateralundersurface side of the tibial component 14 is shorter in theanteroposterior dimension than the medial side, and the top of thetibial component 14 may also be asymmetric.

Anatomically the tibial plateau has a greater anteroposterior dimensionmedially than it has laterally. In order to cover as much of the cutproximal tibia as possible and avoid anterior or posterior overhang ofthe lateral plateau, it is necessary to have a component that is largerin the anteroposterior dimension medially than it is laterally. In oneembodiment, this is accomplished by moving the center of the medialarticular surface posteriorly to compensate for the dimensionaldifferences. In order to achieve full flexion, it is important to havethe medial center of rotation on the tibia (which is a concave segmentof a sphere) more posterior than is currently available with otherdesigns. This allows the proximal tibia, when the knee is flexed beyondapproximately 120-130 degrees, to be positioned anteriorly enough sothat there is no impingement of the posterior edge or portion of themedial tibial articular surface on the proximal portion of the posteriormedial condyle of the femur. Current designs of tibial components 14,which will allow the tibia to move anterior with flexion, either have anon-spherical medial tibial articular surface or the center of rotationof the spherical articular surface is not as far posterior as isprovided by the embodiments described below. However, embodiments of thecurrent invention may be used in combination with any knee replacementdesign that will allow knee flexion to 120° or greater.

Currently-available total knee tibial components 14 that have a fixedcenter of rotation medially have the center of rotation located at aposition that is around 35-45% of the entire anteroposterior dimensionfrom the posterior surface of the tibial component 14. In someembodiments of the tibial component 14, the center of rotation is movedposteriorly so that it is between 18-30% of the anteroposteriordimension from the posterior wall of the tibial component 14.

In the normal knee the medial side of the knee is constrained in thatfor any degree of flexion the position of the medial femoral condylerelative to the tibial articular surface is roughly fixed and does notmove anteriorly or posteriorly a significant amount in the flexion rangeof roughly 20-140 degrees. In contrast, on the lateral side, except forfull extension and flexion, after around 20-40 degrees of flexion thelateral femoral condyle can move anterior and posterior on the lateraltibial plateau. In full functional flexion to 160 degrees and beyond,the lateral femoral condyle may appear to be touching only the mostposterior portion of the opposing tibial plateau or it may contact theplateau more anterior clearly on the flattened portion of the lateraltibial plateau.

Therefore, in embodiments of the tibial component 14, the lateral tibialarticular surface is basically flat in the anteroposterior sense, exceptanteriorly where there is an anterior lip which prevents the tibialcomponent from rotating too far externally and allowing the lateralfemoral condyle to slide off the anterior edge of the tibial component.In some embodiments, the basically flat portion of the lateral tibialarticular surface may comprise between two-thirds and seven-eighths ofthe total anteroposterior dimension of the tibial component 14. In someembodiments, a slight lip may be present posteriorly on the lateralside, however, as long as the fixed center of rotation is positioned asdescribed, no lip is required posteriorly on the lateral side. Thelateral tibial articular surface is either flat or concave when viewedin the frontal plane and, if concave, may or may not be the same radiusof curvature of the opposing femoral condyle or it may have a greaterradius when viewed in the frontal plane. This flat or concave groove isflat on the bottom when viewed in the sagittal plane, except for theanterior and posterior ends as noted above and is generated around apoint that corresponds to the center of rotation of the medial condyle.In some embodiments, the posterolateral tibial articulation may be thesame as described for the medial posterior full flex articulation. Inother embodiments, the medial tibial articular surface may be the sameas, or similar to the flat articular surface described for the lateraltibial plateau. However, the position of the medial articular contact ismainly obligatory while the position of the lateral articular contact isnon-obligatory. Thus, the position of the lateral articular contact islikely determined by the task being performed, by comfort, or byculture.

FIGS. 6A-6D depict a comparison of a prior art tibial component 14'smedial tibial condylar surface 26 and lateral tibial condylar surface 24with an embodiment of the tibial component 14 as discussed above.Specifically, FIGS. 6A and 6B reflect side views of medial and lateralsides of some currently available tibial components 14, respectively,while FIGS. 6C and 6D illustrate side views of medial and lateral sidesof an embodiment of the tibial component 14 as discussed above. It willbe appreciated that a number of varied configurations for the medial andlateral articular surfaces ranging from almost flat, both medially andlaterally, to more conforming, as shown in FIGS. 6A and 6B, have beenused in the past; however, there are none that have either a combinationof a posteriorly-displaced medial articular surface and arelatively-flat lateral articular surface, or a medial femoral full flextibial articulation. These configurations permit the lateral femoralcondyle to move anteriorly and posteriorly as the knee flexes andextends. Other configurations may be provided, so that as long as thelateral tibial articular surface will allow this anteroposterior motion,the lateral tibial configuration does not need to be specifically asshown in FIG. 6D.

The lateral tibial articulation may in some embodiments have noposterior lip, and in other embodiments the posterior surface may slopedownward when it is accompanied by a medial tibial articulation thatprovides for flexion beyond 135 degrees.

In the prior art tibial component 14, the condylar surface has acurvature centered on a fixed point 52. The distance from the fixedpoint 52 (or from the low point of the curvature centered on the fixedpoint 52) to the posterior edge 54 of the tibial component isapproximately 35-45% of the anteroposterior dimension of the tibialcomponent 14. These measurements are similar for the medial (FIG. 6A)and lateral (FIG. 6B) sides of the tibial component 14. Currentlyavailable tibial components 14 have a lip 56.

In the embodiment of the tibial component 14 illustrated in FIGS. 6C and6D, there is no tibial component lip 56. Rather, the medial tibialcondylar surface 26 runs along a smooth arc. As the arc is generated, alow lip may be present in some embodiments and may extend up to andinclude the femoral full flex posterior articulation. The amount of thelip will be determined by the relationship of the center of rotation tothe posterior edge 54 of the tibial component 14. Though the radius fromfixed point 52 to the articular surface in FIGS. 6A and 6C is the same,the distance from the fixed point 52 (or from the low point of thecurvature centered on the fixed point 52) to the posterior edge 54 ofthe tibial component 56 is shorter, at approximately 18-30% of theanteroposterior dimension from the posterior end of the tibial component14, as may be seen in FIG. 6C. With respect to the lateral side of thetibial component 14, in the embodiment illustrated in FIG. 6D, there isboth an anterior lip 58 and a small posterior lip 60. In alternateembodiments, the posterior lip 60 may be omitted as discussed above.

Thus, as has been illustrated with reference to FIGS. 6A-6D, in at leastsome embodiments of the present invention, greater deep knee flexion maybe provided or improved by modifying the tibial articulation, in whichthe center of the conforming medial tibial articular surface of thetibial component 14 is moved posterior relative to what is currentlyavailable. This change alone, with some currently-available femoralcomponents, will increase the amount of flexion achieved when comparedto a standard tibial component. Additionally, in some such embodiments,the overall shape of the lateral tibial articular surface may bemodified. This allows the proximal tibia, when the knee is flexed beyondapproximately 120-130 degrees, to be positioned anteriorly enough sothat there is no impingement of the posterior edge or portion of themedial tibial articular surface on the proximal portion of the medialcondyle of the femur. Therefore, greater deep knee flexion may beachieved. It can thus be appreciated that the use of an embodiment ofthe above tibial component with a conventional femoral component willfacilitate greater flexion than will the use of a conventional tibialcomponent. Similarly, the use of any of the above-described femoralcomponents with a conventional tibial component will facilitate moreflexion than will use of a conventional tibial component with a standardfemoral component.

In some embodiments of the present invention, greater deep knee flexionmay be provided or improved by modifying tibial articulation, in whichthe articulated surface of the tibial component is modified to encourageor limit articulation of the femoral component relative to the tibialcomponent. Examples of such modification are shown in FIGS. 6E-6H.

Referring now to FIGS. 6E and 6F, a tibial component 14 is shown inaccordance with a representative embodiment of the present invention. Insome embodiments, the medial tibial condylar surface 26 of the tibialcomponent 14 is modified to include an articulation feature. Anarticulation feature is generally provided to compatibly interact withan opposing articulation surface of the femoral component. Duringflexion of the knee the articulation surface of the femoral componentinteracts with the articulation feature of the medial tibial condylarsurface to guide or direct the articular movement of the femoralcomponent relative to the tibial component. Thus, in some embodiments anarticulation feature is provided to control articulation of the kneeduring deep flexion.

Various types of articulation features may be used in accordance withthe teaching of the present invention. For example, in some embodimentsan articulation feature comprises an angled articular ridge 400. Thearticular ridge 400 is provided to compatibly interact with an opposingarticular surface of the femoral component. The interaction between thearticular ridge 400 and the articular surface of the femoral componenteffects a change in the articular movement of the femoral componentduring deep flexion of the knee. For example, in some embodiments aninteraction between the femoral component and the articular ridge 400causes the posterior articulation of femoral component to shift whendeep flexion is achieved.

The articular ridge 400 is generally disposed on the posterior surfaceof the tibial component 14 in a general medial-lateral direction 450. Insome embodiments, the articular ridge 400 is disposed or positioned onthe posterior surface at an angle θ that is acute to an anteroposteriordirection 460 of the intercondylar surface 28. Generally, angle θ of thearticular ridge 400 is selected so as to achieve a desired articularshift of the femoral component during deep flexion. In some embodiments,an angle θ of approximately 0° to approximately 90° is selected. Inother embodiments, an angle θ of approximately 10° to approximately 45°is selected. Finally, in some embodiments, an angle θ of approximately20° to approximately 35° is preferred.

The articular ridge 400 may be positioned anywhere on the articularsurface of the tibial component so as to achieve a desired articularshift of the femoral component during deep flexion of the knee. Forexample, in some embodiments the lateral tibial condylar surface 24 ismodified to include the articular ridge (not shown). In otherembodiments, both the medial and lateral tibial condylar surfaces 26 and24 include an angled articular ridge 400. In some embodiments, thearticulation feature comprises a polyethylene coating or layer. In otherembodiments, the polyethylene coating is strictly applied to thearticular ridge 400 and precluded from extending beyond articular ridge400 so as to impinge on the femur during flexion.

Referring now to FIGS. 6G and 6H, a tibial component 14 is shown inaccordance with a representative embodiment of the present invention. Insome embodiments, the medial tibial condylar surface 26 of the tibialcomponent 14 is further modified to include an articulation featurecomprising a spherical articular surface 420. The spherical articularsurface 420 is provided to compatibly interact with an opposingarticular surface of the femoral component. The interaction between thespherical articular surface 420 and the articular surface of the femoralcomponent enable unrestricted, natural articular movement of the femoralcomponent during deep flexion of the knee. For example, in someembodiments an interaction between the femoral component and thespherical articular surface 420 permits a natural posterior articulationof the femoral component when deep flexion is achieved. One of ordinaryskill in the art will appreciate that the tibial component 14 may alsobe modified to permit femoral articulation on the lateral tibialcondylar surface of the tibial component. Additionally, one of ordinaryskill in the art will appreciate that the tibial component 14 may bemodified to permit concomitant femoral articulation on both the medialand lateral tibial condylar surfaces of the tibial component, fordesired applications.

The spherical articular surface 420 may comprise a true spherical shape,or may comprise a parabolic shape. One of skill in the art willappreciate that variations in the surface structure of the articularsurface 420 may be required to provide an articular surface that isoptimally configured for a specific application or use.

The spherical articular surface 420 may be positioned anywhere on thearticular surface of the tibial component so as to achieve a desirednatural movement to the femoral component during deep flexion of theknee. For example, in some embodiments the lateral tibial condylarsurface 24 is modified to include the spherical articular surface (notshown). In other embodiments, both the medial and lateral tibialcondylar surfaces 26 and 24 include a spherical articular surface 420.In some embodiments, the articulation feature comprises a polyethylenecoating or layer. In other embodiments, the polyethylene coating isstrictly applied to the spherical articular surface 420 and precludedfrom extending beyond spherical articular surface 420 so as to impingeon the femur during flexion.

In some embodiments, the opposing surface of the femur and/or femoralcomponent is modified to comprise a concave surface (not shown)configured to compatibly interface with the convex, spherical articularsurface 420 of the tibial component. In other embodiments, the opposingsurface of the femur and/or femoral component is modified to include aconcave groove (not shown) configured to compatibly interface with theconvex, articular ridge 400 of the tibial component. Finally, in someembodiments the polyethylene coating (not shown) or the articularsurface of the tibial component is configured to compatibly interfacewith a desired structure, shape or feature of the opposing femoralsurface, thereby achieving normal knee function and movement throughoutthe knee's range of motion. For example, in some embodiments a tibialcomponent is provided without an elevated, posterior portion orarticulation feature. Rather, the surgeon may elect to leave theposterior portion of the patient's tibia which in turn interfaces withthe femoral component to achieve normal knee function. Thus, in someembodiments a unicompartmental tibial component is provided to achievenormal knee function.

FIGS. 7A and 7B depict modifications to the femoral component 12 and thetibial component 14 to enable deeper knee flexion. Specifically, FIG. 7Adepicts a sagittal sectional view of a knee prosthesis 10 with amodified femoral component 12 and tibial component 14. In FIG. 7A anarea 102 of the femoral component 12 is removed, as represented by thedashed line. This area 102 is above and between the posterior extreme104 and the anterior side 106 of the posterior extreme 104. By removingthe area 102, deeper flexion for prosthetic knee patients is partiallyachievable.

Similarly, with the tibial component 14 in FIG. 7B, a medial side 25 mayappear to be relatively lengthened in the anteroposterior dimensionanteriorly by moving the articular surface 24 posterior and therebyhaving more of the tibial component anterior to theposteriorly-displaced medial articulation. This may give the appearanceof having removed a posterior portion of the tibial component 14 andmoved it to the anterior. A lateral side 27 of the tibial component maybe shortened in the anteroposterior dimension relative to the medialside 25 (i.e., area 100). FIG. 7B illustrates the foregoing in planview. In other words, by posteriorly shortening the lateral side 27(i.e. by removing area 100) of the tibial component 14 and by displacingthe medial articular surface 24 more posterior, deeper knee flexion ispossible. And, these modifications create the opportunity for aprosthetic knee patient to achieve a deeper knee flexion than possiblewith currently-available prosthetic knees.

In at least some embodiments of the invention, greater deep knee flexioncan be achieved by providing an asymmetrical femoral component 12. Theasymmetrical femoral component 12 permits transfer of more than one-halfof the force transmitted across the joint to be transmitted to themedial side, as occurs in the normal knee. Some such embodiments areillustrated with reference to FIGS. 17-18. FIG. 17 illustrates aradiograph of a knee at 160-degree flexion. In the radiograph, the femur32 is viewed in the anteroposterior direction, and a medial condyle 66of the femur 32, a lateral condyle 68 of the femur 32, and a patella 70are visible. As may be appreciated by reference to the Figure, themedial-lateral width of the articulating portion of the medial condyle66 is larger than the medial-lateral width of the lateral condyle 68.Specifically, in the Figure, the medial-lateral width of the articularportion of the medial condyle 66 is represented by X. As may be seen inthe Figure, the medial-lateral width of the lateral condyle 68 isapproximately 75% or less of the medial-lateral width X of the medialcondyle 66.

As may also be appreciated by reference to FIG. 17, the center of thepatella 70 is lateral to the midline of the knee. Specifically, in theFigure the medial-lateral distance between the most medial portion ofthe distal end of the femur 32 and the center of the patella 70 isrepresented by Y. As may be seen, the corresponding medial-lateraldistance between the most lateral portion of the distal end of the femur32 and the center of the patella 70 is approximately 75% or less (73% inthe Figure) of Y. In some embodiments of the invention, the femoralcomponent 12 may mimic the actual physical structure of the kneerepresented in FIG. 17.

In such embodiments of the femoral component as illustrated in FIG. 18,the articular portion of the lateral condyle is, in its medial-lateralwidth, 75% or less than the width of the medial condyle. This allows formore than one half of the force that is transmitted across the joint tobe transmitted to the medial side, which is what occurs in the normalknee. It also allows the patellar or trochlear groove to be lateralizedbecause this groove distally is defined by its position between themedial and lateral condyles. In the normal knee the patella tends to beslightly lateralized on the femur and this lateral displacement of thegroove accomplishes what many conventional total knee replacementsaccomplish by externally rotating the femoral component 12 in the totalknee replacement. In one embodiment the condyles in the frontal planeare seen to be circular with a constant radius. The medial and lateralcondyles do not need to be the same radius, but may both be circularwhen viewed in that plane. When viewed in the sagital plane the condyleswill be seen to have a closing radius posteriorly and anteriorly mayblend into the anterior flange in the embodiments where an anteriorflange is used.

FIG. 18 illustrates a front view of one embodiment of a femoralcomponent 12 in accordance with the described embodiments. In theFigure, illustrative measurements are illustrated to show features ofthe described embodiment, and are not meant to be limiting of thefeatures of the described embodiments. As shown in FIG. 18, the totalmedial-lateral width of the femoral component 12 may be approximately 72millimeters (mm). In this embodiment, the medial-lateral width of themedial femoral condylar surface 20 in the posterior portion of themedial posterior condyle is approximately 32 mm, while themedial-lateral width of the lateral femoral condylar surface 22 isapproximately 22 mm. Thus, in the illustrated embodiment, themedial-lateral width of the lateral femoral condylar surface 22 isapproximately 69% of the medial-lateral width of the medial femoralcondylar surface 20.

In the illustrated embodiment, a patellar groove 72 is defined by thespace between the medial femoral condylar surface 20 and the lateralfemoral condylar surface 22. Because the medial-lateral width of themedial femoral condylar surface 20 is larger than the medial-lateralwidth of the lateral femoral condylar surface 22, the patellar groove 72is displaced laterally, which is what occurs in the normal knee. As maybe appreciated by reference to FIG. 18, the patellar groove 72 may beprovided at an angle as the patellar groove 72 moves from a mostproximal anterior portion to a distal anterior portion to a distalposterior portion and to a proximal posterior portion. For example, theangle of the patellar groove 72 in FIG. 18, as measured from a sagittalplane is approximately 86 degrees.

Thus, the illustrated embodiment shows how a femoral component 12 inaccordance with embodiments of the present invention may assist inachieving deeper knee flexion and, in some embodiments, full functionalflexion, by providing an asymmetric femoral component 12. The asymmetricfemoral component 12 may assist in achieving deeper knee flexion bybetter simulating physiologic loading and patellar tracking. Theasymmetric femoral component 12 allows for more normal loading of thejoint with the medial side taking more of the load than the lateralside. Additionally, the asymmetrical femoral component 12 allows formore anatomically correct lateral tracking of the patella which maydecrease problems of patellar pain, subluxation, and dislocation. One ofskill in the art will readily recognize that in some embodiments thetibial component 14 may be modified to accommodate an asymmetric femoralcomponent 12.

As discussed herein, at least some embodiments of the present inventionembrace providing deeper knee flexion capabilities where the medialfemoral side stays relatively fixed and the lateral side glides forwardsand backwards. While some embodiments embrace a knee with a tibialcomponent that keeps the femoral component relatively fixed on themedial side and able to glide on the lateral side, other embodimentsembrace a knee that is relatively fixed on the lateral side and able toglide on the medial side. This, for example, would apply to the tibialcomponent.

Additionally, while the additional articular surface on the femoralcomponent could be medial, lateral or both, at least some embodiments ofthe present invention embrace its application to use the Tibial andFemoral Full Flex articulations either medially, laterally, or both.

Referring now to FIG. 21 a perspective side view of a knee 200 is shown.In at least some of the embodiments of the present invention, greaterdeep knee flexion may be further provided, improved, or enhanced byremoving a portion of the popliteal surface 202 of the femur 210. Thepopliteal surface 202 may include bone proximal to the posteriorarticular surfaces of the medial condyle, the lateral condyle, or boththe medial and lateral condyles. Resection of the popliteal surface 202may be accomplished by any appropriate method known in the art. Forexample, in one embodiment a portion of the tibia is first resectionedthereby providing sufficient clearance to resect the necessary portionof the popliteal surface 230.

The amount of bone resected from the tibia, the femur or both will varyfrom individual to individual depending upon the specific anatomy of thetibia and the femur. The resectioned popliteal surface 230 providesadditional clearance between opposing surfaces of the tibia 220 and thefemur 210. Specifically, the resectioned popliteal surface 230 preventsan impingement of the posterior articulate surface 250 of the medialcondyle 240 of the tibia 220 on the femur 210 during deep flexion of theknee 200. As such, the knee 200 may flex freely without the tibia 220adversely binding on, or contacting any portion of the femur 210.Additionally, the resectioned popliteal surface 230 may provide flexionexceeding 140°. In one embodiment, the resectioned popliteal surface 230provides flexion exceeding 160°.

Referring now to FIG. 22, a perspective side view of a knee 200 is shownfollowing resection of the popliteal surface 202 to provide theresectioned surface 230. As previously discussed, resection of thepopliteal surface 230 may be accomplished by any appropriate methodknown in the art. However, in one embodiment a resection block 300 isutilized to guide a cutting device 310 in making the resection 230. Theresection block 300 is comprised of a metallic material, similar to themetallic materials previously discussed, and includes an outer surface312, an inner surface 314, and a slot 316. The outer surface 312 iscontoured and adapted to substantially overlap the lateral and medialcondyles of the femur 210. The inner surface 314 includes a plurality ofangled surfaces that mirror the resectioned and shaped surfaces of thelateral and medial condyles of the femur 210. Thus, the inner surface314 of the resection block 300 is adapted to compatibly engage theresectioned surfaces 62, 64, and 366 of the femur 210. The engagedresection block 300 and femur 210 are further secured via a plurality offasteners 320, such as screws. This may not be necessary in all cases.The fasteners 320 are required only to firmly attach the guide to thefemur. In some embodiments, the interaction between the guide and thefemur is such that the guide is held firmly in place without fasteners.In another embodiment, the guide is held in place by any means tofacilitate an accurate resection of the above mentioned area of thefemur.

The interaction between the resection block 300 inner surface 314 andthe resectioned surfaces 62, 64, and 366 of the femur 210 accuratelyaligns the slot 316 with the popliteal surface 202 of the femur 210. Theslot 316 generally comprises an external opening 330 and an internalopening 332. The external opening 330 comprises a first width that isslightly greater than the width 338 of the cutting device 310. As such,the external opening 330 is adapted to compatibly receive the cuttingdevice 310. The internal opening 332 is positioned exactly adjacent tothe popliteal surface 202 and comprises a second width that is greaterthan the first width and approximately equal to the desired width of thepopliteal resection 230. Thus, the walls 334 of the slot taper inwardlyfrom the second opening to the first opening thereby providing a wedgedslot 316.

The cutting device 310 may include any device compatible with the slot316. In one embodiment an oscillating blade 340 is provided. Theoscillating blade 340 includes a shank 342, a cutting head 344 and astop 346. The shank 342 generally comprises a surface that is adapted tocompatibly and securely engage a tool (not shown) capable of moving theblade 340 relative to the resection block 300 and femur 210. The cuttinghead 344 generally comprises a plurality of teeth suitable for removingthe desired portions of the popliteal surface 202 to form the resection230. The stop 346 generally comprises a ferule, a crimp, or some otherfeature that provides a point on the blade 340 that is wider than thefirst opening 330 of the slot 316. As such, the stop 346 is unable toenter the slot 316 thereby limiting the depth into which the blade 340is permitted to enter the slot 316. Thus, the stop 346 acts as a depthgauge to control or limit the final depth of the popliteal resection230. In one embodiment, the stop 346 further comprises a set screwwhereby the stop 346 is loosened and repositioned on the blade 340 tochange the depth into which the blade 340 is permitted to enter the slot316. In another embodiment, the cutting device 310 is a burr bit havinga stop 346 to limit the cutting depth of the burr.

Referring now to FIG. 22A, an underside, perspective view of the femur210 and resection block 300 are shown. In one embodiment, the resectionblock 300 includes a first slot 316 and a second slot 318 separated by aconnecting portion 326 of the resection block 300. The first slot 316 ispositioned adjacent to the medial condyle 66 of the femur 210 and thesecond slot 318 is positioned adjacent to the lateral condyle 68. Eachslot is positioned at a different height relative to the asymmetric,natural positions of the medial and lateral condyles 66 and 68. Thus,the first and second slots 316 and 318 of the resection block 300 areadapted to optimally resect the popliteal surface 202 of the femur 210with respect to the asymmetric positions of the condyles 66 and 68. Inanother embodiment, the first and second slots 316 and 318 arepositioned at equal heights so as to provide a resectioned poplitealsurface 230 that is symmetrical without respect to the asymmetricalcondyles 66 and 68. In yet another embodiment, the positioning of theexternal opening 330 relative to the internal opening 332 of the firstslot 316 is different than the positioning of the external opening 330relative to the internal opening 332 of the second slot 318. As such,the radius of each wedge opening 316 and 318 is different and theresultant contours or shapes of the resectioned popliteal surface 230for the first and second slots 316 and 318 will be asymmetrical. Inanother embodiment, connecting portion 326 is eliminated therebyproviding a single guide slot. In this embodiment, upper and lowerportions of the guide are held in place relative to one another vialateral and medial bridges. The lateral and medial bridges maintain theposition of the upper and lower portions of the guide, as well as definethe outer edges of the slot. In another embodiment, lateral and medialbridges are used to provide multiple slots within the guide.

Referring now to FIGS. 22 and 22A, the popliteal resection 230 is madeby inserting the cutting device 310 into the slot 316 and removing thepopliteal surface 202 to the desired depth, as limited by the stopfeature 346 and the radial limitations of the wedged slot 316. Thewedged shape of the slot 316 permits the cutting device 310 to bepivoted along the radius of the wedge, wherein the contact between thestop 346 and the external opening 330 acts as a fulcrum for the radiusof the wedge. The resultant resection 230 therefore comprises a radialsurface configured and shaped to receive the femoral component 12 of theknee prosthesis. Following formation of the popliteal resection 230, thescrews 320, or other stabilizing methods, and the resection block 300are removed from the femur 210.

Referring now to FIG. 23, a cross-sectional side view of a knee 200 isshown following resection of the popliteal surface 230. The femoralcomponent 12 of the knee prosthesis may be modified to correspond to theresectioned portion 230 of the popliteal surface 202. For example, inone embodiment a portion 212 of the femoral component 12 of the kneeprosthesis is extended and contoured to seat within the resected portion230 of the popliteal surface 202. As such, the posterior articularsurface 250 of the medial condyle 240 of the tibia 220 compatibly andsmoothly interacts with the extended portion 212 thereby furtherenabling the knee 200 to achieve deep flexion. Furthermore, theinteraction between the posterior articulate surface 250 and extendedportion 212 prevents the posterior articulate surface 250 from bindingon a terminal surface 214 of the femoral component and displacing thefemoral component 12 in an anterior direction 300 during deep flexion.In some embodiments of the present invention, the extended portion 212is used in conjunction with a tibial implant having a spherical medialside. In another embodiment, the extended portion 212 is used inconjunction with any knee replacement that will allow knee flexion to120° or greater. For example, in one embodiment a femoral component of aknee prosthesis system is modified to include a piece of metal up theback of the posterior portion of the component to provide an extendedportion 212 compatible with the tibial component of the knee prosthesissystem.

In some embodiments of the present invention including the extendedportion 212, the femoral component 12 does not include an interiorflange or any provision for patella-femoral articulation, as shown inFIGS. 15B and 16B above. As such, the lack of an anterior flange allowthe component 12 to be impacted onto the femur in a relativelyconventional manner, except that the component 12 is implanted afterbeing rotated posteriorly relative to a conventional prosthesis.Additionally, the femoral component 12 can be used without a separatepatella-femoral articular implant. In some embodiments, the component 12is used with a modular flange attached to the condylar implant toprovide femoral articulation of the patella. In another embodiment, thefemoral component 12 is used with separate, unattached patella-femoralimplants. Finally, in another embodiment a separate femoral flange isused for a patella that does not have an implanted component.

Referring now to FIG. 23A, a cross-sectional side view of a knee 200 isshown following resection of the popliteal surface 230, wherein thefemoral component 12 is used in conjunction with a tibial component 14.In some embodiments of the present invention, the above describedfemoral component 12 is used in conjunction with a conventional tibialcomponent 14 that does not have the tibial full flex articulation. Forexample, in one embodiment the above described femoral component 12 isused in conjunction with a tibial component 14 that has the center ofthe medial tibial articulation displaced posteriorly. In anotherembodiment, the femoral component 12 is used in conjunction with atibial component 14 that has the center of the medial tibialarticulation in a position that corresponds with currently availabledesigns. In addition to occupying or lining the resectioned poplitealsurface 230, the extended portion 212 may include additional features tomodify the position of the tibia and the femur during full flexion.

For example, in one embodiment the extended portion 212 is modified torotate the tibia relative to the femur with the knee in full flexion. Inanother embodiment, the extended portion 212 is modified to preventrotation of the tibia relative to the femur with the knee in fullflexion. In yet another embodiment, the extended portion 212 is modifiedto include a spherical surface on its upper or most proximal portion. Assuch, this spherical surface allows the tibia to rotate relative to thefemur in full flexion. In some implementations of the present inventionit may be desirable to have the spherical surface articulate with acorresponding concave surface in the femoral full flex articulation.Such a concavity would offer medial-lateral stability, provide areacontact between the femoral and tibial components, and decreasepolyethylene wear of the prosthesis. Referring again to FIG. 23, in someimplementations of the present invention, the femoral component 12 isused in conjunction with a non-resected posterior portion of thepatient's own tibial plateau to articulate with extended portion 212.

Thus, as discussed herein, the embodiments of the present inventionembrace knee prostheses. In particular, embodiments of the presentinvention relate to systems and methods for providing deeper kneeflexion capabilities for knee prosthesis patients, and moreparticularly, to: (i) providing a flexion attachment to the femoralcomponent of a knee prosthesis or providing an extension of the femoralcomponent, which when integrated with both the femoral component and apatient's femur, results in a greater articular surface area of thefemoral component; (ii) making modifications to the internal geometry ofthe femoral component and the associated femoral bone cuts with methodsof implantation, (iii) providing asymmetrical condylar or articularsurfaces on the tibial component of the knee prosthesis; (iv) makingmodifications to the tibial and femoral components of a knee prosthesis,including removing certain areas of the tibial and femoral components;(v) having asymmetric femoral condyles, including having a closingradius on the femoral component; and (vi) providing femoral and/ortibial full flex articulations, wherein all of the foregoing result indeeper knee flexion capabilities for knee prosthesis patients thanpreviously achievable.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. For example, oneof skill in the art will appreciate that the methods and systems of thepresent invention may be modified for use in unicompartmental kneearthroplasty procedures and prostheses. Thus, the described embodimentsare to be considered in all respects only as illustrative and notrestrictive. The scope of the invention is, therefore, indicated by theappended claims rather than by the foregoing description. All changesthat come within the meaning and range of equivalency of the claims areto be embraced within their scope.

What is claimed is:
 1. A knee prosthesis, comprising: a femoralcomponent configured to replace a distal portion of a femur, the femoralcomponent comprising a first portion; and a tibial component configuredto replace at least part of a proximal portion of a tibia, the tibialcomponent including a first raised articulation feature disposed at afirst posterior edge of the tibial component, wherein the firstarticulation feature comprises a proximal-most portion with a firstarticulation surface disposed posterior to the proximal-most portion,and wherein such first articulation surface is configured to articulatewith the first portion of the femoral component.
 2. The prosthesis ofclaim 1, wherein the first raised articulation feature is disposed on amedial side of the tibial component.
 3. The prosthesis of claim 2,wherein the femoral component comprises a first incurvate articulationsurface disposed at a proximal portion of a posterior medial condyle ofthe femoral component.
 4. The prosthesis of claim 1, wherein the tibialcomponent further comprises a substantially flat articulation surfacethat is configured to articulate with a condylar articulation surface ofthe femoral component, and wherein the tibial component furthercomprises a first raised lip disposed anterior to the substantially flatarticulation surface.
 5. The prosthesis of claim 4, wherein the tibialcomponent further comprises a second raised lip disposed posterior tothe substantially flat articulation surface.
 6. The prosthesis of claim5, wherein the substantially flat articulation surface is disposed on alateral side of the tibial component.
 7. The prosthesis of claim 1,wherein the first raised articulation feature comprises an articularridge that is configured to function as a fulcrum for the femoralcomponent.
 8. The prosthesis of claim 1, wherein the first raisedarticulation feature comprises substantially spherical articularsurface.
 9. The prosthesis of claim 1, wherein the first raisedarticulation feature is disposed on a medial portion of the tibialcomponent, wherein the tibial component further comprises a secondraised articulation feature disposed at a second posterior edge of alateral portion of the tibial component, wherein the second articulationfeature comprises a second articulation surface disposed posterior to aproximal-most portion of the second articulation feature, and whereinsuch second articulation surface is configured to articulate with asecond portion of the femoral component.
 10. The prosthesis of claim 9,wherein the first portion of the femoral component comprises a firstincurvate articulation surface that is configured to articulate with thefirst raised articulation feature, and wherein the second portion of thefemoral component comprises a second incurvate articulation surface thatis configured to articulate with the second raised articulation feature.11. The knee prosthesis of claim 1, wherein the tibial component furthercomprises an undersurface and a stem that extends from the undersurface,wherein the stem is configured to contact an inner, anterior surface ofthe tibia when the stem is inserted into the tibia and the undersurfaceis in contact with a resected surface of the tibia.
 12. A kneeprosthesis, comprising: a femoral component configured to replace adistal portion of a femur, the femoral component comprising a firstportion; and a tibial component configured to replace at least part of aproximal portion of a tibia, the tibial component including: a cuppedarticulation surface; and a first raised articulation feature thatprojects proximally from a first posterior portion of the tibialcomponent, wherein the first raised articulation feature comprises afirst articular surface disposed posterior to a first proximal-mostportion of the first raised articulation feature, and wherein such firstarticular surface is configured to articulate with the first portion ofthe femoral component.
 13. The prosthesis of claim 12, wherein the firstraised articulation feature is disposed on a medial side of the tibialcomponent, wherein the femoral component comprises a first incurvatearticulation surface disposed at a proximal portion of a posteriormedial condyle of the femoral component, and wherein the first raisedarticulation feature comprises a ridge that is disposed at a posterioredge of the tibial component.
 14. The prosthesis of claim 12, whereinthe tibial component further comprises a substantially flat articulationsurface that is configured to articulate with a condylar articulationsurface of the femoral component, and wherein the tibial componentfurther comprises a first raised lip disposed anterior to thesubstantially flat articulation surface.
 15. The prosthesis of claim 12,wherein the first raised articulation feature is disposed on a medialportion of the tibial component, wherein the tibial component furthercomprises a second raised articulation feature disposed at a secondposterior edge of a lateral portion of the tibial component, wherein thesecond raised articulation feature comprises a second articulationsurface disposed posterior to a proximal-most portion of the secondraised articulation feature, and wherein such second articulationsurface is configured to articulate with a second portion of the femoralcomponent.
 16. The prosthesis of claim 15, wherein the first portion ofthe femoral component comprises a first incurvate articulation surfacethat is configured to articulate with the first raised articulationfeature, and wherein the second portion of the femoral componentcomprises a second incurvate articulation surface that is configured toarticulate with the second raised articulation feature.
 17. Theprosthesis of claim 16, wherein the first portion of the femoralcomponent comprises a first incurvate articulation surface that isconfigured to articulate with the articulation feature.
 18. Theprosthesis of claim 17, wherein the incurvate articulation surface isdisposed on a medial posterior condyle of the femoral prosthesis. 19.The prosthesis of claim 12, wherein the first portion of the femoralcomponent comprises a first incurvate articulation surface that isconfigured to articulate with the first raised articulation feature. 20.A knee prosthesis, comprising: a femoral component configured to replacea distal portion of a femur, the femoral component comprising a condylararticulation surface and a first portion; and a tibial componentconfigured to replace a proximal portion of a tibia, wherein the tibialcomponent comprises a first cupped articulation surface that isconfigured to articulate with the condylar articulation surface of thefemoral component, wherein the tibial component further comprises afirst articulation feature disposed at a posterior edge of the tibialcomponent and at a posterior end of the first cupped articulationsurface, wherein the femoral component further comprises a secondarticulation feature that is configured to articulate with the firstarticulation feature of the tibial component, and wherein the firstarticulation feature comprises at least one of: a second cuppedarticulation surface, and a projection that projects from a posteriorportion of the tibial component, wherein the projection comprises anarticular surface disposed posterior to a proximal-most portion of theprojection, and wherein such articular surface is configured toarticulate against the first portion of the femoral component.